The present invention relates to a partial ROM (read-only memory) type optical disk having not only an area for reproduction only in which information is recorded in embossed shape but an area in which information can be rewritten and an optical disk apparatus employing the optical disk, for example, an apparatus for recording and reproducing the optical disk.
In recent years, optical disks are being used as information recording mediums of large capacity. Conventionally, the optical disks have been roughly classified into a type in which information is only reproduced, e.g., a CD-ROM and a type in which information can be additionally recorded or rewritten, e.g., a magnetooptical disk.
However, recently, as indicated in Standardization Specification of ISO CD10090 for a 3.5-inch optical disk for recording digital data, a partial ROM type optical disk provided with both an area for only reproducing information (hereinbelow, referred to as a "ROM area") and an area in which information can be additionally recorded or rewritten (hereinbelow, referred to as a "rewritable area") is proposed. This optical disk includes both a first section in which information is recorded in embossed shape as in the CD-ROM and a second section in which an optical recording film for additionally recording information and guide tracks for additionally recording information are provided. Thus, the first section can be copied in a large quantity of data by stamping as in the CD-ROM, so that a large quantity of programs or data can be widely distributed at low cost.
Furthermore, when a user using the optical disk records additionally his own specific information in the rewritable area, the distributed programs can be customized for the user in setting operational conditions of the programs. Meanwhile, when the user adds his own specific data to the distributed data, the data in use can be updated or extended. As a result, a single optical disk can be used not only as a mere medium for distributing information but as a recording medium whose applications can be expanded variously.
At present, information recording rules for such partial ROM type optical disk having the ROM area and the rewritable area have not yet been determined concretely. Contents and positions of information of a known optical disk are described with reference to FIGS. 1a and 1b by reciting a CD-ROM 1 as an example. FIG. 1a shows contents and positions of information on the CD-ROM 1. As shown in FIG. 1b, all the information on the CD-ROM 1 is recorded by embossed pits 4. The CD-ROM 1 has only a ROM area for reproduction only. Thus, retrieval information 3 for retrieving recorded information such as data or programs 2 is also recorded in embossed shape in the same manner as the data or programs 2.
However, in the case where the partial ROM type optical disk having the ROM area and the rewritable area, in which a large quantity of information has been recorded in the ROM area to fully gain features of optical disks, is widely distributed at low cost, it is desirable that the optical disk can be used in a number of different computers or its applied appliances in common. To this end, information for retrieving information recorded in the ROM area should be capable of being used in the different computers or applied appliances.
In a known optical disk having the ROM area only, for example, a CD-ROM, since information for retrieving information in the ROM area is also recorded in embossed shape by stamping, a method of logically recording the retrieval information (referred to as a "logical specification", hereinbelow) is also fixed. Thus, in the case of the CD-ROM, the retrieval information can be read out under only such a logical specification as described in ISO 9660 referred to as a "CD-ROM specification". Therefore, conventionally, if the same optical disk is used in the different computers or applied appliances employing different logical specifications, the retrieval information is converted on the basis of the logical specification employed in the computer or the applied appliance in use each time and then, is used. In this case, when information in the ROM area is used, a special program for converting the retrieval information is required to be prepared and thus, the information in the ROM area cannot be handled in the same manner as other data used in the computer or the applied appliance in use. As a result, such problems arise that a long period is required for using the information in the ROM area and conversion of the logical specification is necessary. Actually, in the known optical disk having the ROM area only, even when an identical application program or an identical data base is used, a plurality of optical disks are required to be separately prepared for the different computers and its applied appliances in use, respectively.